Gestodene (17-alpha-ethynyl-17-beta-hydroxy-18-methyl-estra-4,15-dien-3-one) is a progestin mainly used as an oral contraceptive, in combination with an oestrogen. This molecule, which was described for the first time in German patent application DE2546062, is a third generation progestin with low androgenic activity.
Gestodene is usually prepared from a hydroxylated intermediate (15-hydroxy-18-methyl-estr-4-en-3,17-dione) which is converted into the desired product by means of a process which comprises the protection of the ketone in position 3 as a ketal, the esterification of the hydroxyl in position 15 and the ethynylation of the ketone in position 17 (see e.g. FR-A-2326927 and EP-A-700926). An alternative route, described by Hofmeister in Arzneim. Forsch. 1986, 36(1), 781-783 or in EP-A-201452, also starts from 15-hydroxy-18-methyl-estr-4-en-3,17-dione, but comprises the protection of the ketone in position 3 as a methyl enol ether, the acylation of the hydroxyl in position 15, and then the introduction of the ethynyl in position 17 (see preparation 2 and example 1b). EP-A-201452 also describes another alternative route comprising the conversion of 15-hydroxy-18-methyl-estr-4-en-3,17-dione into 18-methyl-estra-4,15-dien-3,17-dione, the protection of the ketone in position 3 as a methyl enol ether and then the introduction of the ethynyl in position 17 (see preparation 1 and example 1a). Another process, described in EP-A-1586579, comprises the protection of the ketone in position 3 as a ketal, and the introduction of a phenyl sulphide or phenyl sulfoxide in position 16 which affords the double bond in position 15,16 by elimination.
The crucial step for the synthesis of gestodene is precisely the timely introduction of the double bond at this specific 15,16 position. Introduction of the double bond with concomitant ethynylation in position 17 (as described e.g. in example 1b-d of EP-A-201452) is prone to competition between the elimination of the group in position 15 and the ethynylation in position 17. Introduction at an earlier stage of the synthesis (as described e.g. in preparation 1 of EP-A-201452) may result in impurities being obtained. In each case, this may be detrimental to the overall synthesis yield.
It is therefore an object of the present invention to provide a process for the synthesis of gestodene which is devoid of the drawbacks of the above-mentioned processes. It is in particular an object of the present invention to provide a process which is simple to implement and which makes it possible to obtain gestodene in high purity and yield.